The present invention is directed to improvements in a process for the production of fiber reinforced resin structures, known as pultrusion.
Pultrusion is a technique in which resin-coated fibers are pulled through an elongated heated tube which induces shape to the structure and cross-linkings of the resin. Typically, the fiberous material is fed through a liquid resin bath where individual fibers are thoroughly coated with the resin. Excess material is stripped from the reinforcement by brushes or rollers. The saturated resin reinforced fibers enter an elongated heated die and post curing in an oven immediately following the die have been employed. In the process, the elongated die is relied on as the primary source of heat to effect cure and provides heat to the resin by conduction.
Pultrusion and its general applications are described in "Plastics Design and Processing", May 1976 (pp. 8 and 9), and in U.S. Pat. No. 2,871,911 to Goldsworthy et al, incorporated herein by reference. A modification of the process is described in U.S. Pat. No. 2,948,649 to Pancherz incorporated herein by reference.
Essential to the production of high strength fiber reinforced resin structures is a condition that all the fiberous elements be completely wetted by the resin, that the fiberous elements do not break, and that an absolute minimum of binding resin remain in the finished structure to minimize the distance between adjacent fibers. The pultrusion process, as it has been practiced, has not been found to fully achieve these ends and has been overly costly in the energy required to achieve drawing of a fiber reinforced resin structure into a desired configuration. In addition, the use of elongated dies can result in a disfigurement of the surface of the article due to localized accumulation of cured resin within the interior of the die.